1. Field of the Invention
The present invention relates to a method for manufacturing a ceramic substrate and a ceramic substrate. In particular, the present invention relates to a method for manufacturing a ceramic substrate through a constraint firing step in which a constraining layer is disposed on a base layer that is to be a ceramic substrate after firing and firing is conducted while the shrinkage of the base layer in a planar direction is suppressed, and a ceramic substrate manufactured by the method.
2. Description of the Related Art
In a ceramic substrate that must have high planar dimensional accuracy among ceramic electronic components, firing shrinkage in a planar direction in a firing step or a variation of the shrinkage significantly affects product quality.
To fire a green base layer (ceramic stacked body) that is used to define a ceramic substrate (multilayer wiring substrate) after firing while suppressing the shrinkage in a firing step, a method for performing firing so as not to cause firing shrinkage in a planar direction has been proposed. This is achieved by performing firing (hereinafter referred to as “constraint firing”) while constraining layers 52a and 52b primarily composed of a sintering resistant material, such as alumina, that is not substantially sintered at a firing temperature of a base layer 51 are disposed so as to be in contact with both principal surfaces of the base layer 51 as schematically shown in FIG. 9 (see, for example, Japanese Unexamined Patent Application Publication No. 2002-198646).
In the method of Japanese Unexamined Patent Application Publication No. 2002-198646, the constraining layers that remain that are not sintered after the firing step are physically and mechanically removed by a known method such as wet blasting, sandblasting, or ultrasonic cleaning.
However, where the constraining layers are removed from a sintered base layer by wet blasting or sandblasting after the firing step as described in Japanese Unexamined Patent Application Publication No. 2002-198646, the sintered base layer is damaged and the strength of the sintered base layer is decreased, which may cause cracks. Furthermore, an electrode disposed on a surface of the sintered base layer may be damaged. This reduces the strength of the electrode due to a decrease in the thickness of the electrode that is rubbed off or reduces the connectivity between the electrode and another component due to a decrease in the smoothness of an electrode surface. Consequently, the reliability of the ceramic substrate produced by the method is reduced.